1. Field of the Invention
This invention relates to a method of forming highly insulative thin films, and preferably silicon oxide thin films serving as a memory capacitor or capacitive insulator film on the surface of a semiconductor substrate or printed circuit board when fabricating large-scale integrated circuits (LSIs) and thin film capacitors.
2. Description of the Related Art
Silicon oxide (SiO.sub.2) thin films have conventionally been formed on the surface of a substrate, such as a semiconductor substrate, by one of several methods. One method is vacuum evaporation wherein the silicon oxide thin film is formed by heating silicon oxide by an evaporation source to deposit the evaporation atoms on the surface of a substrate placed within a vacuum unit. Reactive vapor deposition is another method whereby a silicon oxide thin film is formed on the surface of a substrate by heating silicon that is an evaporation substance in an oxygen atmosphere to cause the oxygen to react with the silicon being deposited. Another method is ion beam sputtering by which silicon oxide thin film is formed on the surface of a substrate by injecting an ion beam of an inert gas onto a target material within a vacuum unit utilizing the sputtering effect. Finally, various chemical vapor deposition (CVD) methods such as plasma CVD and thermal CVD have been used.
The breakdown voltage measurements on silicon oxide thin films prepared by the above respective methods indicate such low values as shown by straight line A in FIG. 2. The maximum breakdown voltages are in the order of 10 MV/cm, and this has been an obstacle not only to increasing the capacitance of a thin film capacitor formed by having an electrode film and a silicon oxide film laminated one upon the other in thinner film form, but also to developing LSIs with a high withstanding voltage by which the silicon oxide thin film can operate stably at high voltages. The measured values shown by line A of FIG. 2 were obtained by measuring the circuit shown in FIG. 3. A substrate 11 and silicon oxide thin film 12 are separated by a circuit electrode formed on the surface of the substrate 11. An electrode film 14 is formed on the top surface of the thin film 12.